Satellites have become invaluable tools in such diverse fields as navigation, communications, environmental monitoring, weather forecasting, broadcasting and the like. Hundreds of man-made satellites now orbit the earth, and each year many more are launched from various nations around the world. Moreover, many homes, businesses and government organizations now use satellite systems on a daily basis for entertainment, communications, information gathering and other purposes.
A typical modern satellite has a metal or composite frame that houses a power source (e.g. one or more batteries, solar cells and/or the like) and various electronic components, as well as one or more antennas. The components generally include one or more “transponders”, which are clusters containing one or more radio receivers, frequency translators and transmitters. The total bandwidth of the satellite is provided by the number of transponders, each of which may have a typical bandwidth of 30-70 MHz or so. One type of commercially-available satellite, for example, has a total available bandwidth of 3,528 MHz divided across forty-five C-band and sixteen Ku-band transponders. These transponders are collectively referred to as “the payload” of the satellite.
As shown in FIG. 1, a typical analog transponded communications payload receives multiple uplink beams from the earth or another satellite via an uplink antenna. Each of the received beams is amplified with a low noise amplifier (LNA) and down-converted (D/C) for further processing. The down-converted beams can then be switched, multiplexed (MUX) or otherwise routed and combined prior to upconversion and re-transmission on a downlink beam to the earth or another satellite.
Although some analog transponded satellites may include limited switching and multiplexing functionality, these features are restricted, with switching limited to point-to-point mapping of entire uplink antenna beams to particular downlink antenna beams. This leads to major inefficiencies in the use of satellite bandwidth. A satellite customer typically purchases a “transponder”, or dedicated block of bandwidth on a satellite, for a period of one year or more. Transponder bandwidths are typically fixed in the satellite during design (e.g. at 33, 50, 70 MHz, etc.) and are not finely adjustable after the satellite is constructed. Each transponder provides a connection with dedicated bandwidth and power between two points on the earth (point-to-point), or between one point and broad geographic areas (broadcast). While this arrangement is relatively flexible with respect to the type of signals carried, there are major disadvantages in terms of bandwidth efficiency and transmit power control. Should a satellite customer need slightly more bandwidth than that provided by the transponder, for example, the satellite customer must generally purchase another “transponder-sized” bandwidth segment of 33-70 MHz. Further, if a satellite customer does not use all of its transponder bandwidth, this excess capacity remains unused, wasting a limited and valuable commodity. While some customers have attempted to address this inefficiency by sub-allocating purchased transponder bandwidth to other end users via dedicated terrestrial terminal equipment and extensive special arrangements, sub-allocation typically requires the satellite customer to trust the end users to control their own power and bandwidth usage because no positive control is available to regulate bandwidth and power consumption onboard the satellite. In addition, satellite “pirates” frequently “piggyback” signals onto unused transponder bandwidth, robbing transmit power and degrading communication link performance for legitimate users. Due in large part to these inefficiencies and other factors, the cost of satellite communications remains relatively high compared to terrestrial communications systems, thereby limiting the widespread adoption of satellite communications for many applications.
Satellite payloads have evolved more recently to take advantage of digital technologies for enhanced flexibility and control. Digital satellite payloads generally function in either a channelized manner or a regenerative manner. In the former case, a digital payload simulates traditional fixed analog transponders, but adds the ability to finely divide, control and monitor bandwidth and power allocation onboard the satellite. Digital transponded payloads normally have the ability to perform switching of inputs to outputs in a highly flexible manner, enabling them to act as virtual “telephone exchanges”, where a request for a channel with specific bandwidth/power and antenna characteristics is made, the channel is set up, used, then disconnected. This “circuit switched” capability ensures that only the bandwidth, transmit power and coverage needed is provided, and only when it is needed. Since transponded channels are merely repeated signals, without any modification, transponder payloads can carry any type of signal without regard to format or modulation mode. Unlike transponded payloads, regenerative payloads perform demodulation and remodulation of uplinked signals, recovering and processing not just the user signal, but also the user data embedded within the signal, enabling the payload to act upon it in a desired manner. Embedded data is most often used for autonomous routing in packet based systems and for security functions, as in many government satellites, or both. In particular, error detection and correction can be performed on demodulated data before it is retransmitted, thereby allowing regenerative satellite payloads to generally have better link performance than transponded payloads. These characteristics and others make regenerative payloads the most efficient available in terms of control, bandwidth and power use. Regenerative systems, however, are commonly built to process a single set of signal and data formats that is fixed at design time. Such systems do not typically provide universal signal compatibility as may be available from transponded payload possesses.
As satellite payload evolution continues, satellite customers are progressing from analog transponded to digital transponded to digital regenerative approaches to extract the maximum revenue bearing bandwidth and power from spectrum allocations fixed by law. Digital transponder systems may be relatively easily made to be backward compatible with analog transponder systems since neither system provides onboard data processing. Regenerative systems are generally not backward compatible, however, due to their requirements for specific signal and data types. While the transition from analog transponded payloads to much more efficient digital transponded payloads is clear, the path to provide even more efficient regenerative payload capability without dropping legacy system users or requiring the satellite to carry significantly more processing electronics has been difficult. To avoid loss of operation and to provide continuous revenue flow, existing satellite customers generally desire to transition transponded end users to regenerative services in a gradual manner, over the many-year life span of an expensive satellite asset.
It is therefore desirable to improve the flexibility and functionality of satellite payloads used in data communications in commercial and/or government settings. It is further desirable to provide a satellite payload capable of simultaneously mixing transponded and regenerative modes in a hardware efficient payload, and to provide in-service programmability for regenerative signal and data formats. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.